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Unread 07-13-2002, 10:29 PM   #1
william hendry
Tile Maker, Apprentice Mud Man
 
Join Date: Feb 2002
Posts: 191
What would cause deck mud to become sandy and crumbly in patches on the top after it has cured? I had this happen once before when I used bagged sand mix and thought it was just due to low quality goods. But now I have a bathroom floor that was made with 5:1 sand/portland, thoroughly dry mixed, and had only enough water to bring it to "sandcastle" consistency. On other floors where I've used more portland and a little more water I haven't had the problem.

And now that I'm in this situation, how might I deal with it?
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Unread 07-13-2002, 10:35 PM   #2
John Bridge
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Sounds like not enough water. It can happen. It can also have to do with how fast the mud gets placed and tooled. Don't know, Will. Cat's got into your sand pile and converted it to a litter box?

Suck out the dry pockets, coat the cavity with wet thin set and put more mud in.
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Unread 07-13-2002, 10:50 PM   #3
william hendry
Tile Maker, Apprentice Mud Man
 
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That's what I'm thinking, not enough water. I guess I've been a bit paranoid about putting tooo much water in.

So now I'm just paranoid about the tile not getting a good bond. If it wasn't hydrated enough to begin with, I'm assuming that there may be problem areas that I can't see. In that case will rehydrating later have any benefit? What about using wetter thinset when you set the tile, would that help to hold it all together?
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Unread 07-14-2002, 08:26 AM   #4
Bud Cline
Tile Contractor -- Central Nebraska
 
Join Date: May 2001
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Do you have a garden type sprayer?
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Unread 07-14-2002, 09:02 AM   #5
Brian
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Location: New England
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Hey guys, I found this over at JLC. Invited this fellow "Riley" over to JB as soon as I saw it cuz this looked very interesting. Have a gander at this answer to the same ques:

FROM JLC:

I'll give you my opinion, and this should be interesting because I bet this won't be unanimous. I was trained as a union apprentice and deck mud is one area where I still follow exactly what I was taught. In the intervening years I've changed my orientation on a lot of the things I was taught, but not this one.

Your mud doesn't sound too dry to me - it sounds just fine. I have never used acrylic admix but that shouldn't hurt the mud, if anything it ought to make it better. "Deck Mud" is also known by the name "Dry Pack" and that name is actually more expressive of what we're talking about. It is NOT supposed to be strong. You want to trade off strength in order to make the mud be less brittle.

To give you an idea about the hardness of cured deck mud: if you choose to you can use a hand staple gun to fasten staples into it or a cordless screwdriver to shoot Durock screws into it (without need to drill holes). Of course you don't normally do those things but you CAN.

Deck mud lasts permanently only because of the protective layer of tile or stone which you set to it. By itself it would be worn away by foot traffic.

It has a smooth skin which is created by the flat trowel. I'll tell you what happens when your "worst fear" happens: if the skin starts to break up you suddenly have a crumbly surface. When you start to make layout marks you notice the pencil or sharpie is making the surface crumble, and then you see that your knees and toes are eroding the surface too. At this point if you were to be aggressive with a whisk broom you could wear your way right down to the reinforcing wire. But you don't want to do that. Instead you gently brush or vacuum or blot with a sponge, to pick up most of the powdery crumbs. Then mix some thinset - on the soupy side so it will pour from the bucket - and gently trowel a thin layer. Just enough to impregnate the mud and consolidate its surface. After 2-3 hrs. it will be dry and you can get back on it. Now you won't have any more trouble with that surface being powdery.

What I have described happens about once every five years to me. I am explaining it for two reason. First to bail you out if it does happen. But mainly to show what it reveals about the nature of deck mud. That it has just barely enough cohesive strength to hang together until the tiles are safely set. But once the tiles ARE set they are better off with this mud under them than with a richer stronger mix.

In order not to have that little catastrophe happen the most helpful thing is to cover each section of mud with kraft paper as soon as you're done floating it. If the mud doesn't dry out prematurely there is almost no chance of having a problem with it. (I weight the paper down with tiles or pieces of wood as I go. The next morning I replace them by duct taping the pieces of paper continuously together. I leave it like that until I'm ready to set the floor. Whether it is the next day or next week the mud will be pristine when the paper is removed.)


Whaddaya think? Pretty right on?



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Unread 07-14-2002, 12:37 PM   #6
John Bridge
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I can't argue with that. Guy knows what he's up to.

Beyond that, though, you CAN get little areas of imperfection if the mud is too dry. As Bud indicated, it would hurt to sprinkle the floor. Then clean out the holes and fill them with thin set, or if they are really large areas, bond in more deck mud.
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Unread 07-14-2002, 02:52 PM   #7
Bud Cline
Tile Contractor -- Central Nebraska
 
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This (dry sandy spots) has happened to me, when it does I just spray some water on it and go away. It has always been fine upon my return.

I've always charged it to improper (incomplete) mixing, slapped my hand and moved on.
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Unread 07-14-2002, 10:45 PM   #8
william hendry
Tile Maker, Apprentice Mud Man
 
Join Date: Feb 2002
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Well first, thanks for all the replies; that's a lot of good info. And yes, Bud, I do have a sprayer and the last time this happened to me I used it and that seemed to solve the problem. I probably should just have done the same thing this time but I was getting a bit panicky. I can't imagine anything worse than a client walking around on the floor for a week or so and then having it spontaneously self destruct.

Anyway, what I did instead this time was wipe the surface with a wet sponge in advance of tiling. And then I used somewhat wetter than normal thinset when I tiled. When I went back (with my fingers crossed) to the job today the tile was rock solid. Whew!

As I thought further about what was different between mud jobs that have turned out "right" and those where I have experienced "the crumbles" I realized that the "crumbles" has occured on jobs where the floors were radically out of level (multiple directions) AND where I was also trying to set the floor so that the tile and the adjacent hardwood floor would end up at the same height. I remember being frustrated trying to deal with all these elements and thinking that it was taking me too long to place the mud. That has made me think about something John said about "tooling time". It may just be that the mud is getting too dried out when having to work it a bunch. I'm wondering if maybe a little more water in cases like this might give the mud more open time?

Also, when I tear out really old tile floors built on mud beds, the mud is hard as a rock. Is that due to the cement level or just a loooong curing time?
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Unread 07-15-2002, 06:18 AM   #9
John Bridge
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"Also, when I tear out really old tile floors built on mud beds, the mud is hard as a rock. Is that due to the cement level or just a loooong curing time?"


Don't increase the water. Water weakens cement mortars. Water is your enemy (most of the time.)

If the temperature is not terribly hot, you have about an hour at most to work deck mud. I try to never have it laying around that long.
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Unread 07-15-2002, 06:34 AM   #10
william hendry
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OK, then let me make sure I'm putting the correct amount of water in as I'm doing it now (since I haven't built a sandcastle in some years )

When the mortar is at what I have believed to be the correct hydration I can squeeze it in my hand and it will pack together and retain that shape when I open my fist. However, if I poke at it, it WILL fall apart. It also won't leave my hand wet.

I know this is like trying to explain how to use a hawk from a book () but is that the correct amount of hydration?
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Unread 07-15-2002, 08:32 PM   #11
John Bridge
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That sounds like the correct amount of water. Hydration is the process of curing.
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Unread 07-15-2002, 08:57 PM   #12
Rob Z
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Hi William

The instructions on the bag of dry pack that I use indicates the 60 lb bag needs +/- 0.7 gallons of water. While I haven't precisely checked this, it seems about right. One bucket holds about 60 lbs of dry mix, so maybe you can try to mix a batch using the estimated amount of water and see if it ends up the way you have been mixing it.

For example, if I mix 6 bags at a time, I know I need about 4 gallons of liquid , and fill one bucket up to about 4/5ths as a measuring cup.
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Unread 07-15-2002, 09:28 PM   #13
william hendry
Tile Maker, Apprentice Mud Man
 
Join Date: Feb 2002
Posts: 191
Rob

That sounds in line with how much I'm using. I'm generally mixing about a cubic foot of dry material at a time and use a little over a gallon of water. I'll measure the water more carefully next time and see what I get. Thanks!
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Unread 07-16-2002, 05:53 AM   #14
John K
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Join Date: Jul 2001
Location: Southeast U.S.A.
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Hey guys.
The union guy from JLC seems to have an interesting analysis
of deck mud, but if the mud is that dry wouldn't it have to be extremely thick in order to compensate for the relative
weekness? I would like to find a way to make deck mud no more than 1/2" thick and be as strong or close to, as backerboard. The reason is. Most floors in occupied residences in my area, match up to hardwood and the " market" likes to see everything flush out. Not to mention, ever getting the dishwasher out if the is a problem.
In closing, the use of self-leveler is not an option because of the extreme over pricing of the product. Any thoughts will be appreciated..


John K
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Unread 07-16-2002, 06:37 AM   #15
william hendry
Tile Maker, Apprentice Mud Man
 
Join Date: Feb 2002
Posts: 191
Question: If the mud is crumbling, and the tile is stuck to the crumbling mud, what would prevent the tile from coming up with a bunch of crumbling, "delaminating" mud securely thinset to the bottom of it?
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